I'd like to re-finish them, without fully stripping them first. Can it be done at all? Can I just wipe something like wipe-on polyurethane on them?
Sure, you can do that, but it will probably look like junk. Long story short, there is no shortcut way to refinish wood. All forms of refinishing (that look nice, anyway) will require removing the existing finish to some level.
Without a picture showing exactly what you're working with, it's hard to tell exactly what to do in your situation. I'm going to assume that your cabinets are finished using polyurethane based on the time of life you're describing and the general usage of that finish.
Based on my experience with degraded finishes, I'm assuming you have some peeling or flaking of the finish. If they've been in constant use for 25 years, you probably have some rub-through as well.
The rub-through might be a little easier to deal with if all you're looking to do is wipe on a new coat of finish. There is no flakiness to remove, so there is a smooth transition between the finished and non-finished parts, at least as far as tactile smoothness goes. However, the cabinets have 25 years of patina on them in the form of accumulated dirt and grime. Finishing over that will not have a good effect.
If the finish is flaking, you will have to remove the flakes if you want any hope of a nice finish when you're done. And, if you're removing flakes of old finish anyway, you might as well go ahead and remove it all in one go.